Smokie start up

my discovery 300TDI has a ticking sound at 'tick' over it also has a ticking noise when being driven but this isnt very noticable. i changed the rocker shaft, lifters and pushrods and it still does it so i bought a cheap auto stethascope and i have located the ticking to the vacum pump on the side of the engine ! but at a touch over a hundred quid ill stick with the free ticking. them automotive stethascopes are brill for tracking down unwanted noises. i didnt think it would be much cop but its brill and it only cost about a fiver.